Robust Adaptive Control Of Aerospace Vehicle Re-entry Based On Fuzzy Predictive Control

Aerospace vehicle (ASV),which is the next generation reusable flying vehicle, has very important martial value and civil value. During its hypersonic re-entry flying, big angle of attrack (AOA) bring the fast change of ASV's speed, attitude and attitude, its equation subjects to serious nonlinear and coupling characteristic. Moreover, ASV subjects to the unkown disturbancea and uncertainties, so the design of fly control system of ASV is an attractive subject in the modem control area. In this dissertation, the adaptive predictive control methods of MIMO uncertain system are designed and used to solve the control problems involving in the fly control system of ASV.First of all, a simulation model of an ASV is presented, which includes the centroid motion of ASV and a six degree-of-freedom kinetic equations and motion equations. Its open-loop dynamics and stability characteristics demonstrate that the proposed model can behave the intricate nolinear, coupling and fast time-varying of ASV's re-entry, so it can be used in the following theory research and evaluation of advanced guidance and control methods.Secondly, a kind of finite horizon predictive method is used to design the re-entry guidance control law of ASV under hypersonic fly condition. With the restrictions of ASV, the re-entry corridor is defined. By choosing an appropriate drag acclertaion as the reference trajectory, the ASV's guidance predictive law is designed by talyor series expansion. Simulation results of the ASV guidance system indicate the acceptable performance of the designed law to track the reference signal.Thirdly, according to the complex nonlinear and uncertain ASV kinetics motion, a class of MIMO uncertain nonlinear predictive control shceme is investigated based on fuzzy reconfigurable systems, and its valid application on the robust adaptive flight control system of ASV with unkown model. By adjusting the fuzzy weight parameters on-line, the fuzzy system is used to approximate the unkown function and construct the nonlinear predictive control law. Furthermore, on the purpose of alleviating the conservatism of controller, an adaptive robust controller is constructed to compensate approximation error of fuzzy system. Using Lyapunov theory, it has been proven that the overall system were uniformly ultimately bounded. Finally, the flight control system of ASV under hypersonic condition is designed by the proposed method. Simulation results demonstrate the effectiveness of the method.In the following, the inner uncertainty and unkown disturbance of ASV are considered, which are regarded as composite disturbance. Under the guidance of theoretical analysis, a novel predictive control structure is developed by combining the current predictive method with the well-known compensation idea, the composite disturbance is compensated and elimeated by fuzzy systems, so the performance of the nonlinear predictive controller is guarraneted . Moreover, the concept of"variable universe"is introduced into fuzzy system, according to the tracking error, the contraction and expansion factor of variable universe fuzzy controller is adjusting, which lead to the improvement of response quality of fuzzy system.Theoretical analysis illustrates that the accurate approximation to the uncertainty can enchance the performance of the controller greatly. Combining with the previous research, this thesis investigates a class of nonlinear robust predictive control scheme based on fuzzy disturbance observer, the scheme can be provided as an effective method to a kind of nonlinear uncertain systems. Using the useful information of the controlled system, the method realized the accurate approximation and control, so the performace of controller is enhanced. By Lyapunov stability theory, the adjusting law of fuzzy disturbance observer is given, moreover, the ultimate boundness of the tracking error and oberserve error has been proven.Finally, considering the slide mode control and predictive control, this article puts the sliding surface into the quadratic index, and gets the sliding mode control law through the minimum of the index, so the nonlinear robust adaptive controller is constructed which is based on predictive sliding mode. The proposed scheme is highly robust as slide mode control, and has the virture of optimization as contious predictive control. Applying the fuzzy adaptive system to the controller, the prior knowledge about the upper bound of uncertainty can be removed, so the chattering of sliding mode is weakened greatly.